The invention relates to a spreading device for a pneumatic application of brake sand on rail-mounted vehicles, comprising an air source and a sand container as storage container for the brake sand or the spreading material, an outlet at the lower end of the sand container, a connecting pipe to a mixing container provided for air-charged swirling of the spreading material to form a sand stairway and a dispensing device disposed on the mixing container for the specific dispensing of the spreading material onto the rails in front of the wheels.
Spreading devices have been known for more than 100 years and in rail-mounted vehicles provide for an improvement in the traction and braking properties or prevent spinning or sliding of the wheels by compressed-air assisted application of sand onto the rails in front of the wheels.
The spreading material used is usually coarse natural quartz sand whose grain size distribution is designed for the mechanical requirements for increasing friction and for a reproducibly the same spreading quantity per unit time in the case of pneumatic application. However, ceramic sands or other free-flowing mineral particles in suitable grain size distribution and spreading quantity in each case can also be used. The proposed spreading device is advantageously suitable for all sand-like or free-flowing types of spreading materials.
Among the known spreading systems, various pneumatic spreading systems have been developed over time which differ in functional principle or mode of operation according to the available air pressure range.
For example, rail vehicles of the main-line railways are usually equipped with an on-board compressed air network which can provide compressed air at 3 to 10 bar for spreading devices. However, the generation and supply of compressed air in this magnitude is relatively expensive and this should usually be used sparingly for spreading devices. For this reason, spreading devices with available high compressed air potential preferably operate according to the ejector pump principle in order to use the impulse effect of a high-pressure free jet effectively and as efficiently as possible. A spreading device which, for example, operates according to the ejector pump principle has been disclosed with the utility model specification DE 20 2014 004 632 U1.
Known spreading devices of a different type produce a defined excess air pressure in the sand container and convey by means of the conveying flow produced inter alia by pressure equalization, an air-sand mixture usually via a so-called sand stairway, through a corresponding application device onto the rail in front of the wheels. Inter alia for cost reasons, such systems operate with a lower air pressure, for example, up to a maximum of 3 bar.
A sand spreading device of the aforesaid type with excess air pressure in the sand container has become known, for example, from the Unexamined Laid-Open Patent Application DE 41 14 515 A1 which is intended to assist the effect of the spreading sand conveying flow with a compressed air jet nozzle directed towards the inlet of the sand staircase. On account of the relatively long flow path of the air through the sand, where the sand can be additionally held up as a result of the acute-angled deflections, the resulting energy losses must be compensated by higher pre-set air pressure.
A sand spreading device of the aforesaid type with excess air pressure in the sand container has also become known from the utility model specification DE 83 28 423 U1 in which the compressed air source in the form of a compressor operated with 24 Volts of direct current is disposed inside the sand container. In this case, this sand container is connected via a gently ascending riser pipe to the perpendicularly downwardly directed downpipe which in turn is connected via a sanding hose to the spreading pipe in the region of the rail vehicle. In a sealed housing, the compressor is disposed on or on the sand container, the pressure hose of which is guided into the sand container and ends at a distance from the riser pipe, where the compressed air flowing out of the pressure hose presses the sand into and through the riser pipe whereupon the sand is dispensed via the downpipe. The relatively small cross-sectional area of the riser pipe is intended to prevent unintentional sanding as a result of sand liquefaction due to vehicle vibrations but can also have the disadvantageous effect that the sand in the riser pipe can compact and hold up.
A pneumatic sand spreading device which is to be operated with air in the lower-pressure range of 0.5 bar has become known from the Unexamined Laid-Open Patent Application DE 41 22 032 A1. In this case, a metering device flange-mounted to the sand container has a pot-shaped metering container. An outlet pipe projects into the metering container through its base, the upper end thereof projects below a fixed bell at a distance from the inner bell base. Located at a distance from the base of the metering container and underneath the bell is an air-permeable sintered metal plate through which compressed air can be blown into the sand container and under the bell. Located approximately at the highest point of the sand container is an elbow with downwardly pointing opening and an exhaust pipe which in turn is connected via an adjustable throttle to the outlet pipe. The blown-in air flow is therefore divided. Some of the air flows through the sand in the sand container and through elbow, exhaust pipe, throttle and outlet pipe into the open. The other part of the air flow under the bell, is intended to mobilize the sand and discharge it through the outlet pipe into the open or onto the rail. In this case, the throttle is intended to independently control the respective distribution of the quantitative fractions of the air flow. A disadvantage with this device is that depending on the filling height in the sand container the sand can compact and hold up under the bell due to its own weight. Another disadvantage is that the amount of air which is intended to flow through elbow, exhaust pipe, throttle and through the sand in the sand container is also dependent on the fill level of the sand in the sand container.
In addition, in known spreading devices the disadvantage can occur that even coarse spreading sand can at least partially lose its pourability due to wetting with moisture and in the case of corresponding holding up or compaction as a result of its own weight or vibrations, can no longer be mobilized pneumatically and dispensed as desired. Scientific investigations have additionally shown that undercooled coarse sand tends to conglomerate or form clumps when moist air flows through it.
In addition, known spreading devices which are operated by an on-board compressed air network independently with compressors usually do not have “industrially dry” air. When using spreading materials which contain moisture-sensitive or even hygroscopic components, this can have the result that spreading materials tend to clump when moist compressor air flows through.
The object is therefore to provide a spreading device with which a uniform quantity of free-flowing spreading material can be continuously dispensed securely and blown reliably onto the rails in front of the wheels in which air with relatively low pressure is required for reliable blowing out or dispensing of the sand or spreading material and with which an unintentional emergence of sand or spreading material when the spreading device is not is use is largely eliminated.